Method and apparatus for controlling the liquid seals on steam sterilizers



Nov. 24, 1953 A H WEBSTER 2,660,512

METHOD AND API 'ARATUS FOR CONTROLLING THE LIQUID SEALS ON STEAM STERILIZERS Filed- Jan. 14, 1949 2 Sheets-Sheet l /2 V 9 5 f l7 P'Q :7 "I

" Inventor flaw/vase M/flawre 2 E I fitiorneys Nov. 24, 1953 A. H WEBSTER ,660,512 METHOD AND APPARATUS FOR CONTROLLING THE LIQUID SEALS 0N STEAM STERILIZERS Filed Jan. 14, 1949 2 Sheets-Sheet 2 Attorneys Patented Nov. 24, 1953 UNITED STATES METHOD AND APPARATUS FOR CONTROL- LING THE LIQUID SEALS ON STEAM STERILIZERS Alexander Hyde Webster, London, England, assignor to R. W. Webster and Company Limited, Abbey Ironworks, Waltham Cross, England, a British corporation Application January 14, 1949, Serial No. 70,987

Claims priority, application Great Britain February 6, 1948 Claims.

This invention relates to sterilising machines such as used for sterilising milk or other liquids or foodstuffs in bottles or other containers.

The object of the invention is to devise a sterilising machine which will be more stable as regards its operating conditions than machines heretofore used, thus improving and rendering more uniform the quality of the finished product, reducing breakage of the containers due to temperature and other changes, and rendering the machine more flexible, and of greater utility than heretofore. The various features of the invention set out herein may advantageously be embodied in machines adapted to operate at the same temperature as known machines, 1. e. at about 224 F., and moreover have further advantageous application to machines designed to operate at higher temperatures, e. g. at 230 F., as adapted for some purposes in accordance with modern practice.

The invention accordingly consists in a method of stabilising the operation of a sterilising machine having a sterilising chamber sealed by a head of liquid, wherein a part of the sealing column is subjected to positive cooling.

The invention further consists in a sterilising machine comprising a closed sterilising chamber sealed by a head of liquid, and means for positively cooling a length of the sealing column of liquid.

The invention will be clearly understood from the following description of forms (given, however, merely by way of example) which it may assume, and this description will be more readily followed by reference to the accompanying drawings, wherein:

Figure 1 is an end elevational View, and Fig. ure 2 an end sectional elevation of a sterilising machine according to the invention, while Figures 3, 4 and 5 are sectional views of details of the invention.

The general construction of known sterilising machines, for example British Patent No. 377,890, to which the present invention is directed will be appreciated by reference to Figure 2 of the accompanying drawings, representing a bottle sterilising machine used, for example, to sterilise milk. Bottles I previously charged with the material to be sterilised are carried on an endless band 2 through a sectional chamber 3 filled with steam, maintained at a temperature of approximately 224 F., the passage of each bottle through the heated chamber occupying some -40 minutes. The inlet and outlet of the heated chamber comprises U-shaped passages 4, 5, filled with water whereby the chamber is sealed from the atmosphere, and a difference of water level in the two limbs of each U-shaped passage as shown provides a pressure head for maintaining the pressure inside the heated chamber necessary to keep the steam therein at the desired temperature of approximately 224 F. The bottles are passed through the water in the two sealing ducts, 4, 5, when entering and leaving the heated chamber 3, and the water in the inner or pressure side of the inlet sealing duct 3 is heated to the desired temperature by a steam coil, or by direct injection of steam at inlet 6 or otherwise, whereby the pressure tank becomes filled with wet steam at the desired pressure and temperature. The heating is thermostatically controlled to maintain the pressure and temperature at their desired values, and means are also provided automatically to maintain the desired head of water in the inlet and outlet sealing tanks in the event of variation of displacement of water therein arising, for example, from interruption of the transit of bottles into the machine on the carrier. It will be appreciated that although the inner limbs of one or both U-shaped sealing tanks are heated, the external limbs, on account of access of the atmosphere are at a substantially lower temperature and the temperature gradient is established in each sealing tank 4, 5. In particular the outgoing bottles enter the outlet sealing tank at the sterilising temperature and in passing through this tank transfer their heat to the water therein, maintaining the temperature gradient therein at prearranged values, without need for application of heat thereto from any external source.

After passing out of the outlet sealing tank 5 the bottles are carried through a cooling tank I sectioned to form a U-shaped conduit, and during this stage of transit the bottles are cooled by a flow of water introduced by a pipe 8 into the outlet side of the cooling tank I and flowing in the direction indicated by the arrows to an overflow or outlet aperture in the Wall of the inlet side of tank l. After this cooling the bottles may again be carried through a cooling trench 9 located beneath the machine, Where they again move against an inflow of cooling Water introduced by a pipe [0 to the trough 9. The water introduced into the cooling tank 1 may be drawn from the trough 9 and lifted in pipe 8 by means of a suitable pump Illa. After traversing the trough 9 the bottles are removed 3 from the conveyor at the outfeed I! located, for example, near to the infeed I2.

It will be apparent that the temperature maintained within the tank 3 is determined by the head of water maintained in the sealing ducts l, 5. The water in these ducts is subject to variations of temperature, and consequential variations of density, by changes of external conditions, alterations of the rate of infeed of bottles and other causes, and there is considerable danger that the sealing columns in tanks 4 and 5; will become unstable, the balance thus be disturbed, and the desired head thus not maintained. This danger is present at whatever workmg temperature the machine is operated'('e.'g. at the temperature of 224 F. heretofore used), and may become increasingly difficult to control if the machine is to operate at a higher temperature, say 230 F. In particular water at high temperature in the inner or pressure limbs of the inlet and outlet seals'may-fl'ow to the opposite limb of the seal where it ma'yrise rapidly, through the cooler and denser water therein, and, upon reaching a zone of reduced pressure, tend to convert instantaneously to steam, thereby completely disturbing the balance of the seal.

This danger is'to some extent, but not fully, controlled in the inlet seal by the fact that the water in the pressure limb is artificially heated under thermostat control which reduces the heating if abnormal conditions, resulting in undue rise of temperature, are set up. The water in the pressure limb of theoutlet seal is heated by the continuous immersion of hot bottles from the holding chambers. It is not readily possible to reduce or control the temperature of this limb if rising temperature conditions prevail and in existing machines no means are provided for that purpose.

According to thepresent invention the aforesaid danger of instability in a sterilising machine is eliminated from; or controlled in, either or both the inlet and outlet seals of the machine by providing means for -cooling a part of the liquid column contained-in the outer limb of the seal. This cooling'is'controlled, preferably automatically, so as-not-only to maintain the average temperatures, andthetemperature gradient of the column at-anyde'sired values, but-also to provide a blanket of-cooledorcooler water at the top of the column which will serve to stabilise the column, and-willhave the additional advantage, in the inlet seal, of acting as a tempering zone for initially receiving the incoming bottles thus avoiding or reducing breakage which-might otherwise occur upon immersing the bottles in water at comparatively hightemperature.

The cooling may bea'ffected by any convenient means including-separately or in combination, aircoolingof the exterior surfaces of the sealing tank over a selected area by natural convection and/or by an artificial draught from fans or the like: the direct injection of cooler water into the sealing column, or the passage of water or other convenient-cooling media through coiled pipes immersed in the column.

In'a preferred embodiment of the invention shown in Figure 1 of the drawings herewith, cooling 'is effected by the direct injection of water into the top of the water column in the inlet and outlet seals, allowing it to flow downwards through the sealing columns'for a prearranged distance and to flow out from the sealing-tanks through suitable cutlets provided. -While this cool injected water may 1 be obtained from any convenient source, it is preferred according to the invention to take it as shown from the overflow of the bott1ec001ing tank and to convey it by suitable piping to the top of the water column of the inlet and outlet seals.

As shown in Figures 1 and 4 water from the cooling tank 7 is conveyed by an overflow pipe l3 to an overflow tank M from which it is Withdrawn and raised to a level at or above the top level of the water in the outer limbs of the sealing tanks bya'pump l5 through a pipe I6 communicating by a T-junction with each of thesealing columns. The cold water thus introduced sinks into and cools the upper portion of'each'sealing column. A pipe I8 (Figures 2 and 3) secured in the wall of each sealing tank 4, 5, and open at its uppermost point, projects downwards in each sealing column and serves at its lower end as an overflow outlet for excess Water in the column. It will be seen therefore that the sealing column is cooled-betweenits uppermost level and the lower, open, end of overflow pipe 18, which may extend, asshown, to nearly one third of the depth of the column.

According to a further feature of the invention cooler water may be tapped from the cooling tank (in addition to water taken from thenormal overflow outlet I3) at a point somewhat lower than the overflow outlet l3, i. "e. reached by the cooling water at anearlier period ofits fiOW through the cooling-tank.

For this purpose a pipe l9 passing through the wall of the cooling tank 1 may project downwards to a comparatively-low level-in'th'e cooling tank (Figures 1 and'4), and externally of the tank may be joined to a pipe 120, open atrits upper end, which feeds into the'overflow'tank I4. It will be'clea'r that'the'water tapped by means of pipes 19, 20, will be cooler Zthan'that passing through the overflow pipe l3, ancl'the two supplies intermix'in the'overflow tank l'dto provide water at "an intermediate ltemperature determined bythe relative rates 'of flowbf=the two supplies. Suitable control valves (not shown) may be provided at'the two outl'ets through which cooling water is taken from :the "cooling tank "so that by suitable adjustment-the relative amounts of water taken-from the' two points can be varied to modify the-temperature of 'tlie: mixture fed to the sealing column, according to working requirements. The total rate of flow ofcoolingwater to the inlet seal -ispreferably' controlled by thermostats ll provided in order to maintain the thermal balance of the machine asfdictated-iby the load-imposed on the machine: determinediiby the rate of input of bottles.

As-in known sterilising machines, a machine according to the -invention, as described above, may be providedwith asafetydevice designed tolimit theinternalpressure-of :themachineito below a prearranged maximurn' val-ue. fineform of such a safety device is described inEritish patent 'speeificationNo. 431,944. In the prese'nt invention it may take the-form of a'U-shape d tank communicating with the' pressure chamber of the -machine and providing an "alternative water seal having a pressurehead adapted to break before the sealing'depth in the pressure limb of themain sealing-tank is forcedto zero. This safety tank is preferably 1 well spaced from the heated water columnsandother.heated.elements of the machine in: order that it'will not be subject to variations of *temperatureliable to render it unstable or todisturbthe limiting safety conditions for which it is set.

One form which such a safety tank may assume is shown in Figure 5. The level 2i of water in one limb of this tank 22 is subjected to the steam pressure in the holding chamber 3 of the machine, and represents the lower working level of water in the pressure limbs of the sealing tanks t and 5. The level 23 represents the lowest point of the partitions in the sealing tanks t and and is below the open end of a pipe 2 which is normally immersed in the water on the pressure side of tank 22. This pipe 2 communicates with an overhead venting tank 25 from which another pipe 26 communicates with the sealing limb of safety tank 22. It will be clear that if pressure in the machine increases unduly the water level 2| in tank 22 will be depressed but will open the lower end of pipe E l before it reaches the sealbreaking level 23 of the partitions in tanks i and 5. When pipe li iis thus opened steam enters forcing water into the venting tank 25 from which it is returned to the sealing column. This escape of steam reduces the internal pressure of the machine to a safe condition and the seal is restored.

If desired the gap 21 between the sealing tank 5 and the cooling tank '5 (Figure 2) may be closed at its sides to form a tunnel through which air, by convection and/or by fan pressure, may pass to assist in cooling the adjacent walls of the tanks.

If any of the forms of the invention described above are used to sterilise articles which are normally at a low temperature when fed into the machine, the articles, e. g. glass bottles, may become damaged by sudden substantial rise oi temperature when entering the inlet seal, despite the fact that the upper portion of the sealing column is cooled. To overcome this dinlculty there may be provided a pre-heating chamber or column through which the articles are passed immediately before entering the inlet seal. This pre-heating chamber or column may be maintained at a temperature, or with a temperature gradient, whereby the articles are heated to a temperature approaching that at the entrance of the inlet seal, thereby avoiding abrupt temperature variations of the articles as they are fed in. This pro-heating chamber may be heated by water drawn from the hotter side of the outlet cooling tank, e. g. as it is circulated. towards the pipe it for feeding to the sealing columns, or through a separate pipe system.

It will be appreciated that known stcrilising machines such as hereinbefore described, comprising a heated sterilising chamber sealed by one or more liquid columns, can readily be adapted to incorporate the features of the present invention, and it is within the scope of the invention to provide attachments for known sterilising machines whereby the advantages of the invention will be introduced. Such attachments may comprise, for example, a set of pipes corresponding to pipes i3, l5, l5, l8, l9 and 25 shown in Figure l (the pipes corresponding to the crossmembers of the T-junction of pipe it being fitted with, or adapted to receive, thermostat control devices, l'i, also provided), a mixing chamber simillar to tank id, and a pump corresponding to pump l5. These attachments may be suitably dimensioned and shaped to fit to the appropriate sections of an existing sterilising machine, and it will be seen that by cutting suitable apertures in the walls of the machine the attachment pipes can readily be secured thereto without difficulty.

From the above description it will be seen that appropriate temperature control is exercised on the head of a liquid sealing column by injecting liquid from another source, e. g. another point the circulatory system of the apparatus. By this means the liquid density at the top of the column is maintained at a value necessary to guard against rupture of the seal. In general, when steady conditions are reached, the injected water will be cooler than the liquid at the head of the sealing column, but under some temporary conditions (e. g. if the infed bottles reach the column at a substantially reduced temperature) the temperature of the head of the column may be reduced to such an extent that the injected water is, for the time being, warmer than the head of the column. Under these conditions the injected water will tend to heat the head of the column and will continue to do so until, under the thermostat controls provided, additional heat is supplied to the system, (c. g. at the steam heating coils), and, by conduction through the seal, re-established steady conditions with a modified heat gradient in the column.

If desired the form of the invention shown in Figures 1 and 2 herewith may be modified by inserting an additional pipe connection between the pipe 3 and the overflow tank it, the outlet from this additional pipe into the tank it being controlled by a -lioat valve operable in accordance with the liquid level in tank it. This ar rangement ensured proper operation of the apparatus when (e. g. due to a gap in the line of bottles or other articles being passed through the machine) displacement or" water in cooling tank '5 is reduced and the level of water therein falls below the overflow outlet it. (Figure 4).

in these circumstances the tank is would be completely drained. This diiiiculty is overcome by provision of an additional supply line from pipe 8 as described above. If desired this arrangement may be further modified by providing an adjustable valve in place of the float valve, allowing an adjustable amount of the supply to tank It to be taken continuously from pipe 55 and thereby facilitating adjustment of the water temperature in tank Hi. It will be noted that these modifications allow adjustment of water flow through the cooling tank "5' without interfering with the water supply to tank i l and from there to the sealing columns i and. 5.

It will be seen that the invention as described above provides a steriiising machine adapted to remain stable and to operate satisfactorily under the temperature conditions described, but it must be understood that the invention is not restricted solely to the constructional details of the forms described, which may be modified in various ways to fulfill different working conditions and requirements encountered, without departing in any way from the scope of the invention.

What I claim is:

l. A method of steam sterilizing articles in a closed heated steam sterilizing zone having an inlet sealed by a water-filled U-shaped sealing zone having an inner leg in communication with said sterilizing zone and an outer leg in communication with the atmosphere, passing the articles to be sterilized serially through the outer and inner legs of the sealing zone into the steam sterilizing zone, and forcibly positively cooling a fixed length of the upper portion of the column of water in the outer leg of the sealing zone from the top thereof down to a point about one third of the depth of the column of water in the outer leg.

*2. 'A :method of steam sterilizing accoizding :to claim 1 in which ;the cooling of :the fixediength of the :column .of .water' is effected :by :introducing cold'water into the-outer l-egat the uppermost portiono'f theicolumnrif waterin'said outer leg, and :discharging water from :the column :of water ate point aboutione thirdfof .the depth of the column of water.

13. A method "of -steam.zsterilizing according to claim 1 in which 'thettcooling of 1 the fixed length of the columni'of Water is FEfiQCtEd :by rpassingza cooling medium in heat exchange :-;relation with said fixedlength iof waterinthe outer leg of thetsealingtnone.

4.:A steam "sterilizing machine comprising a closed :heated :steam v:sterilizing ;,chamber, U- shaped. inlet and outlet: conduits ,eachrhaving an inner legiin communication with saidchamber and an outer leg in communication with the atmosphere, :columns of water in said ,conduits, a coolingrtank containing water .at lower-temperature. than the \waterin said sealing. columns, means for conveying articles to .:be sterilized through said inlet conduit, into and through said sterilizing chamber, out therefrom through said outlet conduitand into and through said-cooling tank;a water transfer conduit providing communication between said cooling tank-and the top of the sealing'column of water intheouter leg :of ;said inlet :conduit, .pump means in :said water: transfer conduit for-effectingrmovemeneof water from :said cooling atank ;to the v,topxof :the column :of :water vin nthe ;o,uter' leg ,of said inlet conduit, and :means .including ;an outlet :in the outer leg at' a level :below: the level at" which :.cold water is :delivered ,by :said water transfer conduit to 'said :sealing column through which -;o.utlet water 'escapesat "substantially the same .rate:;as saidzcold water isideliveredto ,saidzsealing 1:01- umn, :.for :maintaining ;a .jsubstantial'ly constant levelof-waterinzsaid inletsealing column.

.5. Asterilizing :machine according :to claim :14 wherein the water :transfer vconduit communicates with,; and-transfers .'wtater:ifr.om said: cooling tank'tozthe topof .thelsealing column in1therQuter leg of the outlet conduit,-,as well as to thetODiof thev sealingcolumn in the .outer "leg of thervinlet conduit.

ALEXANDER HYDE WEBSTER.

References Cited in the file of this patent UNITED-STATES PATENTS Number Name Date "2,154,978 Galvin .Apr.18, I939 FOREIGN PATENTS Number Country Date 377,890 Great-Britain Aug. 14,1932 

1. A METHOD OF STEAM STERILLIZING ARTICLES IN A CLOSED HEATED STEAM STERILLIZING ZONE HAVING AN INLET SEALED BY A WATER-FILLED U-SHAPED SEALING ZONE HAVING AN INNER LEG IN COMMUNICATION WITH SAID STERILLIZING ZONE AND AN OUTER LEG IN COMMUNICATION WITH THE ATMOSPHERE, PASSING THE ARTICLES TO BE STERILIZED SERIALLY THROUGH THE OUTER AND INNER LEGS OF THE SEALING ZONE INTO THE STEAM 